Single electron transfer (SET) is a process in which organic reagents act as an electron donor/ acceptor in making C-C, C-, N-, S- bonds via single electron transfer reduction/ oxidation process. Radical cyclization is an efficient strategy for the synthesis of structurally complex, biologically active and pharmaceutically important carbo- and heterocyclic ring systems.1 Transition metals promote radical reactions by two distinctive pathways, namely, i) oxidative cyclization of carbanion and ii) reductive cyclization of carbocation (Figure 1).2


Figure 1. Oxidative and Reductive mode of transition metal mediated SET cyclization

Recently, our group developed one-pot synthesis of structurally complex cyclopropane-fused bicyclic amidine using CuBr2-mediated oxidative cyclization of carbanion as a key strategy (Scheme 1).3 Transition metal mediated SET oxidative/reductive cyclization is an advanced tool in cascade reaction for the construction of complex organic molecules. In this presentation, applications of transition metal salts as SET oxidants in the synthesis of complex organic frameworks will be discussed. Besides, application of metal-free SET oxidative reactions involving photo-SET oxidation and unconventional electrochemical radical reactions in organic synthesis will be discussed.


Scheme 1. One-pot synthesis of cyclic amidine via ketenimine
References:
1. (a) Romero K. J.; Galliher, M. S.; Pratt, D. A.; Stephenson, C. R. J. Chem. Soc. Rev. 2018, 47, 7851. (b) Yan, M.; Lo, J. C.; Edwards, J. T.; Baran, P. S.; J. Am. Chem. Soc. 2016, 138, 12692.
2. Plesniak, M. P.; Huang, H.-M.; Procter, D. J. Nature Rev. Chem. 2017, 1, 0077.
3. (a) Veeranna, K. D.; Das, K. K.; Baskaran, S. Angew. Chem., Int. Ed. 2017, 56, 16197. (b) Veeranna, K.D., Das, K. K.; Baskaran, S. Chem. Commun., 2019, 55, 7647. (c) Veeranna, K.D., Das, K. K.; Baskaran, S. Org. Biomol. Chem., 2021, 19, 4054.